1. Field of the Invention
The invention relates to a piston for use with a direct injection, spark ignition engine.
2. Background Art
A direct fuel injection engine is typically designed to improve fuel economy at low engine loads by providing stratified charges in a combustion chamber of the engine. With a stratified charge, a near stoichiometric or fuel-rich air/fuel region in a generally lean of stoichiometry air/fuel mixture is formed near a spark plug.
Typically, stratification is achieved by providing a deep recess or bowl in a piston of the engine, and by providing tumble and/or swirl air flow into the combustion chamber. As fuel is injected into the combustion chamber, the fuel impinges against the bottom or side of the bowl and cooperates with the motion of the air in the combustion chamber to produce the stratified charge.
While the deep bowl aids in the formation of the stratified charge, the stratified charge may not be optimally positioned with respect to the spark plug. As a result, combustion may be unstable and incomplete. Furthermore, the deep bowl increases surface area of the piston, which results in increased heat loss to engine coolant via the piston during the expansion stroke. The increased heat loss causes increased fuel consumption and reduced torque output.